An examination of mineral deposits in a coastal cave on the Spanish island of Mallorca shows evidence of rapid rises and declines in sea level as the planet warmed and cooled.

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Reporting in the journal Science, University of Iowa researchers said that studies of the mineral, calcite — deposited by sea water on the inside of a seaside cave, like rings on a bathtub — showed that roughly 81,000 years ago sea levels jumped by more than 6 feet a century during a warm period, and then dropped during a subsequent cooling cycle at a similar rate — 66 feet per 1,000 years. CO2 levels during that period were lower than they are today, but temperatures rose because the Earth’s orbit placed it in a position where it received more of the sun’s energy, the study said.

Jeffrey Dorale, a geoscientist at the University of Iowa and the lead author of the paper, said that his study underscored similar findings from other researchers about the volatility of sea level rise as the Earth’s ice sheets form and melt. "It’s fair to say that this means glaciers may change somewhat faster than we once inferred," said Dorale. "It does suggest there can be very fast melting and very fast ice building at times when CO2 levels were lower than now."